This invention relates generally to a plastic composite pipe structure and more particularly to a crush-resistant, leakproof, plastic composite pipe structure.
Various types of pipe structures have been proposed for use under a variety of environmental conditions. Conventional smooth-bore pipe, for example, is widely used in the conveyance of fluids, the sections of which may be joined end-to-end by means of bolted flanges, sleeve couplings, bell and spigot fittings, and the like. However, in order to withstand high hydraulic pressures and/or to possess high crush-resistance when utilized in underground applications, the wall thickness of conventional smooth-bore pipe must be increased substantially. In many cases, an excessive amount of material must be employed to fabricate the pipe, resulting in excessive weight and uneconomical costs.
Corrugated pipe has been proposed to overcome some of the disadvantages of smooth-bore pipe. It has been found, however, that although the corrugated configuration improves crush resistance it also contributes to poor hydraulic characteristics in the transmission of fluids.
Composite tubes as disclosed, for example, in U.S. Pat. No. 3,330,303, comprise an inner smooth-walled tube and an outer corrugated tube and possess improved crush resistance. Sections of such composite tubes are joined by means of a resilient collar fitted over the outer corrugations of adjacent sections. Alternatively, joining is effected by shaping the outer corrugated tube to provide a bell and spigot arrangement. In both instances, the smooth-walled inner tube is joined in a simple butt fit. Such an arrangement may serve as a satisfactory conduit for electrical wires and cables but would be highly susceptible to leakage in the conveyance of fluids, particularly those under pressure.